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Directed Evolution Method in Saccharomyces cerevisiae: Mutant Library Creation and Screening
Published on: April 1, 2016
A Saccharomyces cerevisiae mutant with increased virulence
Robert T Wheeler1, Martin Kupiec, Paula Magnelli
1Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, 9 Cambridge Center, Cambridge, MA 02139,USA.
Abstract:
Saccharomyces cerevisiae, bakers' yeast, is not a pathogen in healthy individuals, but is increasingly isolated from immunocompromised patients. The more frequent isolation of S. cerevisiae clinically raises a number of questions concerning the origin, survival, and virulence of this organism in human hosts. Here we compare the virulence of a human isolate, a strain isolated from decaying fruit, and a common laboratory strain in a mouse infection model. We find that the plant isolate is lethal in mice, whereas the laboratory strain is avirulent. A knockout of the SSD1 gene, which alters the composition and cell wall architecture of the yeast cell surface, causes both the clinical and plant isolates to be more virulent in the mouse model of infection. The hypervirulent ssd1 Delta/ssd1 Delta yeast strain is a more potent elicitor of proinflammatory cytokines from macrophages in vitro. Our data suggest that the increased virulence of the mutant strains is a consequence of unique surface characteristics that overstimulate the proinflammatory response.
Insights
Saccharomyces cerevisiae, or bakers' yeast, can cause infections in immunocompromised individuals. A specific gene knockout (ssd1) significantly increases yeast virulence by altering cell surface characteristics and overstimulating immune responses.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Saccharomyces cerevisiae (bakers' yeast) is typically non-pathogenic in healthy individuals.
- Increasing isolation from immunocompromised patients necessitates understanding its virulence.
- Questions arise regarding the origin, survival, and virulence in human hosts.
Purpose of the Study:
- Compare the virulence of different Saccharomyces cerevisiae isolates in a mouse model.
- Investigate the role of the SSD1 gene in yeast virulence.
- Determine the mechanism by which altered yeast surface characteristics affect host immune response.
Main Methods:
- Infection of a mouse model with clinical, plant, and laboratory yeast strains.
- Genetic knockout of the SSD1 gene in yeast isolates.
- In vitro assessment of cytokine induction in macrophages.
Main Results:
- Plant isolate was lethal in mice; laboratory strain was avirulent.
- SSD1 gene knockout (ssd1 Delta/ssd1 Delta) increased virulence in clinical and plant isolates.
- Hypervirulent ssd1 Delta/ssd1 Delta strain potently elicited proinflammatory cytokines from macrophages.
Conclusions:
- Yeast virulence is strain-dependent and can be modulated by genetic factors like SSD1.
- Altered cell surface characteristics in ssd1 Delta/ssd1 Delta mutants enhance virulence.
- Overstimulation of proinflammatory responses by unique surface features contributes to increased yeast pathogenicity.
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